Change language to avoid talking about object operations

[zimeon]

The spec is explicitly supposed to be about "the object-at-rest" (https://ocfl.io/1.0/spec/#note).

I think thus think that the comment in Version Directories "Operations that add a new version to an object must follow the version directory naming convention established by earlier versions. " should be rewritten to something for the object-at-rest like "The version naming convention MUST be consistent across all versions."